The Remark about an Analogy between Magnetocaloric Behaviour of Type II Superconductors and Ferromagnetic Materials

Abstract

This paper concerns mainly the magnetocaloric behaviour of ferromagnetic materials, which have a phonon system and a magnon system mutually interacting. Our earlier calculations [1, 2] described the thermodynamic dissipation of energy evoked by an increase in the external magnetic field in an adiabatically isolated system. The change of sign of the magnetocaloric effect was deduced in the vicinity of the magnetic phase transitions [1, 3, 4]. The increase in magnetic field to the critical value Hc in the direction perpendicular to the easy anisotropic axis of a ferromagnetic material causes the magnetization to turn and saturate in the direction of the external magnetic field and it can also result in a decrease in temperature (the sign of magnetocaloric effect becomes negative). In Ref. [2] it was shown that a similar behaviour can be expected also in the case of superconductors of type II in the mixed state. A change of sign of the magnetocaloric effect in superconductors can be expected near the transition from a superconducting state into a state of normal conductivity. In this case the transfer of energy between collective excitations of crystalline and vortex lattices will be responsible for the negative magnetocaloric effect.